FM part of fui file (instruments)

[brossaip]

I want to program the FM part of OPL4 in the Moonsound for MSX. I'm using furnace as an instrument designer. Thus I need a way to know the fui format to extract the parametres ADSR, etc. to configure OPL4.

I've seen that the file is described in https://github.com/tildearrow/furnace/blob/master/papers/newIns.md. I've created some instruments varying few parameters to discover if the bytes that are changing are the same as are described in the documentation.

Unfortunately my experiments that not match the theory. After the FM command, I have a header of 6 bytes in place of 4 as is documented. I mean, the parameters of detune and mult are 6 bytes away from FM in place of 4 as stated by the documentation.

Hasn't the documentation been updated? Where can I find more information?

I also don't understand the flah of op enabled, the first byte after FM and the rest of the header.

[brossaip]

LTVA has answered me in Discord and highlighted that a feature uses 2 bytes for the code and 2 for the block length. This is why I had the offset of two bytes.

LTVA has also told me that the flag op enabled is a characteristic for OPN chips.